The use of submerged torpedoes for various underwater missions is well known. Further, it is well known that torpedoes can be launched from aircraft, surface ships or from submarines. The particular launching platform is, of course, an important consideration in the design and configuration of the torpedo. The present invention is primarily concerned with underwater launched torpedoes and the constraints within which such torpedoes must operate. More particularly, the present invention is concerned with propeller propulsion systems for such torpedoes.
It is well known that whenever turbulent flow develops on a propeller blade, the efficiency of the blade diminishes significantly. Further, for underwater operations the phenomenon of cavitation, which is an aggravated form of turbulence, also reduces the blades efficiencies. Accordingly, one design feature which can be used to avoid these unwanted effects is to operate the propeller at reduced rates of rotation, i.e. lower RPM. However, with lower RPM, in order to obtain the same propulsive force it will generally be necessary to have a greater surface area for the propeller blade.
For tube launched torpedoes, such as is generally the case when a torpedo is launched underwater, the configuration of the torpedo must be compatible with the launching tube. An example of such a torpedo, which is constrained by the confining dimensions of a launch tube, is provided in U.S. Pat. No. 3,565,028 which issued to Hancks et al. for an invention entitled "Steerable Self-Propelled Submersible". Further, this invention and the invention disclosed in U.S. Pat. No. 2,094,997 which issued to Lucich for an invention entitled "Propelling Mechanism for Torpedoes" both disclose counterrotating propellers as a way for controlling the torque which is generated during propulsion of their respective torpedoes through the water. The propellers disclosed for these inventions are, however, relatively short. And this is particularly so for the tube launched torpedo disclosed in the Hancks et al. patent. Consequently, in order to develop significant thrust, these propellers must operate at relatively high RPM with the consequent drawbacks mentioned above.
As mentioned earlier, one way in which to avoid the disadvantages of a high RPM propeller is to make the propeller larger and let it operate at the lower RPM. For underwater torpedoes, however, the torpedo must be compatible with a launch tube. With this in mind, the present invention recognizes that a torpedo with a propulsion system that can be reconfigured with long blade propellers after launch can operate at lower RPM. Further, the present invention recognizes this can be done by allowing the propeller blades to extend from the torpedo after it has been launched. Although U.S. Pat. No. 2,847,960 which issued to Endrezze for an invention entitled "Radial Expanding Missile Torpedo Fins" discloses extendable fins for a torpedo it does not address the problems confronted by a rotating propeller.
In light of the above, it is an object of the present invention to provide a low RPM propulsion system for a submerged vehicle which can be launched under water from a tube having a restrictive diameter. Another object of the present invention is to provide a low RPM propulsion system for a submerged vehicle which provides suitable propulsive force for the vehicle while minimizing turbulent flow over the propeller blades. Yet another object of the present invention is to provide a low RPM propulsion system for a submerged vehicle which is reliable and predictable in its operation. Still another object of the present invention is to provide a low RPM propulsion system for a submerged vehicle which is easy to use, relatively simple to manufacture, and comparatively cost effective.